The present invention relates to methods and apparatus for supplying to consumers vaporized gas from a storage tank such as an above-ground or below-ground tank, cylinder, or the like, storing the gas in liquified form.
Many techniques are known in liquified-gas storage and distribution systems for supplying the xe2x80x9cheat of vaporizationxe2x80x9d necessary for converting a liquified gas to a vapor. One technique supplies the heat of vaporization by convection with respect to the ambient heat, but such a technique requires large heat-convection surfaces according to the demand for the vaporized gas. Another technique provides an external vaporizer for heating the liquified gas and converting it to vapor form as the gas is outputted from the storage tank or recirculated back to the vapor, but such techniques involve large installations, and therefore large installation and maintenance expenses in preparing and maintaining the infrastructure. These techniques also require vapor/liquid separation devices which introduce reliability and safety problems.
An object of the present invention is to provide a novel method, and also a novel apparatus, for supplying vaporized gas from a liquified-gas storage tank.
According to one aspect of the present invention, there is provided a method of supplying vaporized gas from a storage tank storing the gas in liquified form in a lower liquid region and having a vapor region thereover, the method comprising: providing a source of external heat; adding directly to the liquified gas in the storage tank only sufficient heat from the source of external heat to cause the heated liquified gas to remain mostly in the liquified state but to enable the internal heat of the liquified gas within the storage tank, together with the influx of ambient heat, to supply the heat of vaporization for vaporizing, within the storage tank, the liquified gas according to the the consumer demand therefor; and supplying vaporized gas to the consumer, according to the consumer demand, directly from the vapor region of the storage tank.
According to further features in the preferred embodiments described below, the external heat supplied by the source of external heat is controlled by a microprocessor according to the temperature and pressure of the liquified gas within the storage tank, and the liquid/vapor phase diagram of the respective gas.
According to further features in one preferred embodiment described below, the source of external heat includes a heat exchanger having a first fluid circuit through which a heating fluid is circulated, and a second fluid circuit through which a portion of the liquified gas from the liquid region of the storage tank is circulated, heated by the heating fluid, and returned to the storage tank. The heating fluid, heating the portion of the liquified gas circulated through the heat exchanger, vaporizes less than 50%, preferably 0-20%, of the so-heated liquified gas which is returned to the storage tank.
According to another aspect of the present invention, there is provided apparatus for supplying vaporized gas on consumer demand, comprising: a storage tank storing the gas in liquified form in a lower liquid region thereof and having a vapor region thereover; a source of external heat in heat-exchange relation to the liquified gas in the storage tank for supplying heat thereto; a control system for controlling the source of external heat to cause it to add- directly to the liquified gas in the storage tank only sufficient heat to cause the heated liquified gas to remain mostly in the liquified state but to enable the internal heat of the liquified gas within the storage tank, together with the influx of ambient heat, to supply the heat of vaporization for vaporizing within the storage tank the liquified gas according to the consumer demand therefor; and a supply line communicating with the vapor region of the storage tank for supplying vaporized gas to the consumer according to the consumer demand.
The method and apparatus of the present invention thus eliminate the need to deal with vapor, and thereby avoid the need for expensive vapor/liquid units and separators since the liquid/vapor separation is performed within the storage tank itself. Moreover, the method and apparatus minimize the external heat needed for supplying the gas in vapor form, and thereby reduce the heating expenses and the pollution caused be providing the additional heat. The invention may therefore be used for supplying vaporized gas to a consumer in an efficient and reliable manner, and by using equipment which is relatively compact and inexpensive to install and to maintain.
Further features and advantages of the invention will be apparent from the description below.